JP2009515340A - Optical device featuring a textured semiconductor layer - Google Patents

Abstract

Semiconductor sensors, solar cells or emitters or their precursors have a substrate and one or more textured semiconductor layers deposited on the substrate. This textured layer increases light extraction and light absorption. Texturing in the region of multiple quantum well layers greatly increases internal quantum efficiency when the semiconductor is polar and the quantum well is grown along the polar direction. The electroluminescence of the LED of the present invention is dichroic, yields a discolored LED, includes a white LED, and does not use a phosphor.
[Selection] Figure 5c

Description

[Cross-reference with related applications]
This application claims the priority of US Provisional Application No. 60 / 732,034, filed Oct. 31, 2005, entitled “Optical Device Featuring a Textured Semiconductor Layer”. This application is also a continuation-in-part of US application Ser. No. 11 / 107,150, filed Apr. 15, 2005, entitled “Optical Device Featuring Textured Semiconductor Layer”. This is a US Provisional Application No. 60 / 562,489 filed on April 15, 2004 entitled "Formation of III-Nitride Template Textured for Production of Efficient Optical Devices"; US Provisional Application No. 60 / 615,047 filed Oct. 1, 2004, entitled “Formation of Textured III-Nitride Templates for Efficient Optical Device Production”, January 2005 Claims priority based on US Provisional Application No. 60 / 645,704, filed 21 days, entitled “Flat, pleated quantum well based nitride LED”.
Further, this application is a partial continuation application of PCT / US / 2005/012849 entitled “Optical device featuring textured semiconductor layer” filed on April 15, 2005. Each of the aforementioned prior applications is hereby incorporated by reference in its entirety.

[Statement on Federal Aid or Development]
Part of the research that led to this invention was supported by the US Government provided under Contract No. DAAD 19-00-2-0004 and US Department of Energy Grant No. DE-FC26-04NT42275 awarded by the US Army Research Office It was carried out by. Accordingly, the United States government has certain rights in this invention.

"Background Technology"
A light emitting diode (LED) is a semiconductor optical device capable of generating light in the infrared, visible, or ultraviolet (UV) region. LEDs that emit in the visible and ultraviolet are made using an alloy of gallium nitride (GaN) and its indium nitride (InN) and aluminum nitride (AlN). These devices generally consist of p and n-type semiconductor layers arranged as pn junctions. In standard LED devices, the semiconductor layer is grown uniformly on a polished substrate, such as GaAs or sapphire. A typical semiconductor layer is formed by gallium nitride (GaN) doped to be a p- or n-type layer.

  An important figure of merit for an LED is its internal quantum efficiency (IQE) and light extraction efficiency. For a typical LED, IQE depends on many factors, such as point defect density, Auger process and device design. For nitride LEDs grown along the polar (0001) or (000-1) direction, internal efficiency is also reduced due to quantum well strain between n and p doped layers caused by internal electric fields. . The light extraction efficiency of the GaN-based reference LED is determined to be 4% per surface from Snell's law. LEDs typically have several quantum wells made from small energy gap semiconductors (wells) and wide band gap semiconductors (barriers). Visible LEDs use indium gallium nitride (InGaN) as a well and GaN as a barrier. Ultraviolet LEDs use different compositions of AlGaN for both wells and barriers. The internal quantum efficiency (IQE) of a nitride semiconductor-based LED device grown along the polar direction is reduced by an electric field applied to the quantum well. This phenomenon is called the quantum confined Stark effect (QCSE). QCSE affects the light emission of the LED, shifting the emission wavelength red and reducing the photoluminescence intensity. The somewhat smaller value of light extraction efficiency in the reference LED is a result of the high refractive index at the exit interface of the semiconductor layer.

  Some approaches attempt to increase light extraction from the LED. For example, in a GaAs LED, light extraction is affected by the absorption of radiation in the GaAs substrate. To alleviate this problem, one can use epitaxial lift-off and wafer bonding techniques to move the GaAs LED structure to the transparent substrate. Another approach, combined with the use of substrate mirrors, including optimization of LED surface geometry (eg, inverted pyramids with sharp edges) pushes the extraction limit up to 30%. Another approach involves the use of a continuously changing refractive index transmissive material to reduce back reflection in the boundary region. Some of these approaches have manufacturing limitations and the last one is subject to rapid indicator material degradation over time.

  Recently, an increasingly attractive approach is photon extraction from a thin film surface that is randomly microtextured. LEDs based on GaAs have a record of an external quantum efficiency of 44% at room temperature (Windish et al., 2000), and significant improvements in extraction efficiency have been made. In this reference, the textured surface was formed after LED growth using a lithographic method. Even in such a case, most photons were still extracted from the radiation cone within the critical angle corresponding to the flat surface. Therefore, there is still a large space to improve the extraction well below this value.

  GaN-based visible and ultraviolet (UV) LEDs and other III-nitride materials are widely used as white LEDs for full-color displays, automotive lighting, consumer electronics backlighting, traffic signals, solid state lighting. It has been broken. Various approaches are used in the direction of white LED formation. One approach is the use of tri-color LEDs (RGB), and hybrid methods such as UV LEDs in combination with tri-color phosphors, or either bi- or mono-color phosphors with blue and blue / red LEDs approach. When the efficiency of 200 lm / W or more is a commercially attractive semiconductor lighting, the white LED has recently achieved 30 lm / W.

  The latest internal quantum efficiency (IQE) for electron-hole pair conversion to photons in nitrided LEDs is ~ 21% (Tao, 2000). Therefore, IQE needs to be increased to 60% -70% for applications related to solid state irradiation. To achieve this, many improvements in state of the art are required. For example, bandgap engineering (quantum wells, quantum dots) must provide the best use of carrier conversion for photons. Also, improvements in the various layers of the LED structure are required to reduce defect density, thereby improving carrier transport. Such improvements reduce heat generation, increase device life, increase color stability, and reduce consumer price for life.

[Summary of Invention]
The present invention provides a device for use as a light emitter or sensor or as a solar cell. For emitters of this invention based on polar semiconductors such as III-nitrides, the internal quantum efficiency (IQE) and light extraction efficiency are improved over conventional devices. For sensors or solar cells, the efficiency of coupling the light source into the device is also improved. In one embodiment, the semiconductor material is deposited as multiple layers, starting with the textured first semiconductor layer being deposited on the substrate during growth. In one embodiment, this layer is randomly textured when grown on the substrate to have a textured surface morphology. The substrate and textured layer can be used as a template for growth of multiple semiconductor layers. For example, the device may comprise a second layer deposited over the first textured layer. These layers can be deposited with p and n dopants to form a pn junction light emitting diode (LED). The textured light emitting layer enhances light escape. The first semiconductor layer preferably serves as a barrier layer on which the quantum well is grown. Each of the plurality of semiconductor layers is similar to the texture of the first growth layer, and thus the outer surface of the LED from which light is extracted has approximately the same texture as the initial semiconductor layer.

  Multiple quantum wells with multiple barriers and quantum well layers are preferably deposited on top of each other, alternating with multiple semiconductor layers, each replicating its original texture. Textured replication replicated through the barrier and well layers changes the position of the quantum wells so that their surfaces are not orthogonal to the [0001] polar direction. Thus, quantum wells substantially maintain their rectangular well shape. This is because they are not distorted by an internal electric field due to polarization. As a result, the hole and electron wave functions overlap, leading to efficient recombination, thus dramatically improving IQE.

  The apparatus of the present invention includes a substrate such as silicon (Si), gallium arsenide (GaAs), gallium nitride (GaN), aluminum nitride (AlN), indium nitride (InN), aluminum gallium nitride (AlGaN), indium gallium nitride, It can consist of indium aluminum nitride, indium gallium aluminum nitride (InAlGaN), silicon carbide, zinc oxide, sapphire and glass. The sapphire substrate may be nitrided before a layer is deposited thereon.

  The semiconductor layer grown on the GaN template or on another layer during the entire growth process can be deposited by any suitable process. Examples of such deposition processes include hydride vapor phase epitaxy (HVPE), molecular beam epitaxy (MBE), organometallic compound vapor phase epitaxy (MOCVD), liquid phase epitaxy and laser ablation. The layer of the semiconductor device can be made of a III-nitride material such as GaN, AlN, InN or any combination of these materials. The substrate can be textured prior to layer growth or by selecting appropriate growth conditions such that the first semiconductor layer on the substrate has a textured surface.

  The semiconductor layer includes a dopant, which can be p-type or n-type. Exemplary dopants include beryllium, selenium, germanium, magnesium, zinc, calcium, Si, sulfur, oxygen, or combinations of these dopants. One layer is a monocrystalline or polycrystalline layer. The device of the present invention can include several p and n-type layers and one or more buffer layers that generally facilitate layer growth. An exemplary buffer layer is a GaN semiconductor layer. The buffer layer is deposited on the substrate or between the semiconductor layers.

  The semiconductor layer for the device of the present invention is deposited to a thickness of about 10 Angstroms (Å) to 100 microns (μm). The GaN template and deposited layer texturing has an average peak-valley distance of about 100 nanometers (nm) to 5 μm.

The present invention also provides a method for fabricating the semiconductor device of the present invention. The method includes providing a substrate and growing a first semiconductor layer on the surface of the substrate. The first layer is naturally textured randomly when grown, or is randomly textured by the textured substrate surface. The substrate or first layer can then be used as a template to deposit other semiconductor layers having the same texture as the template. In a preferred embodiment, the fabrication method comprises growing several quantum wells. The multiple quantum well is textured by the first layer, the substrate, or a combination thereof.
Other features and advantages of the present invention will become apparent from the following detailed description of the invention, taken in conjunction with the accompanying drawings.

Detailed Description of the Invention
One or both of the external light extraction efficiency and the internal quantum efficiency (IQE) are improved in the LED and photodetector of the present invention. Light extraction efficiency is improved by a textured emission surface that is typically replicated by the process of applying a layer from the initial semiconductor substrate layer. Furthermore, the LED of the present invention has a two-color electroluminescence spectrum whose color is controlled by a bias current through the LED.

  By controlling the growth rate and using an appropriate deposition procedure, a textured surface layer can be formed on the initial substrate. This texture is replicated through those layers as subsequent layers are applied, resulting in an emissive layer with significantly improved light extraction efficiency. Texturing of the final surface can also be accomplished by texturing the underlying substrate separately or by using an unpolished substrate decorated with deep grooves. This is because the wafer is usually cut from the ingot using a saw.

  Improvement of the internal quantum efficiency (IQE) of the LED is achieved by incorporating multiple quantum wells (MQW) in the pn junction. As a result, electrons and holes injected from the p and n sides, respectively, are better confined and thus more efficient recombination occurs.

  When a semiconductor device including a quantum well is grown in a polar orientation, the resulting quantum well is distorted, resulting in electron and hole separation. As a result, the electron-hole region is located far away, reducing the efficiency of electron-hole recombination that generates light. The LED of the present invention overcomes this deficiency by growing quantum wells on the textured surface. In this way, the quantum well is not distorted and thus the electrons and holes in the well recombine more efficiently.

  In one embodiment of the LED according to the present invention, the LED is formed on the substrate 2. A textured semiconductor layer 4 is deposited on the substrate, as shown in FIG. 1 and FIGS. 2a and 2b and discussed more fully below. This layer is textured when grown on the substrate and has a textured surface topology (or morphology) 10. The substrate and textured layer are used as a template for growth of multiple semiconductor layers to form an LED. Such textured AlN templates can also be used to produce UV LEDs. For example, one device may comprise a second layer deposited on the first textured layer. These layers can be doped to form a pn junction for a light emitting diode (LED). Suitable dopants include selenium, germanium, zinc, magnesium, beryllium, calcium, Si, sulfur, oxygen or any combination thereof. Each of the semiconductor layers can be textured by replication from the first growth layer and its textured surface and have a textured emission surface with improved extraction efficiency.

  In another embodiment, as shown in FIGS. 3a, b, 4a, b and FIGS. 5a, b and discussed more fully below, a multiple quantum well comprising a plurality of barriers and quantum well layers comprises: Alternating semiconductor layers are deposited on top of each other between the n and p doped layers of the device. As used herein, the term “quantum well” relates to a quantum well layer combined with an adjacent barrier layer. When multiple quantum wells are grown on a first layer, they are textured by replication from the textured surface of that layer.

  In most cases, a variable thickness n-doped AlGaN cladding layer is grown between the textured layer and the quantum well.

  Suitable substrates used for the growth of the first layer are known in the art. Exemplary substrates include sapphire, gallium arsenide (GaAs), gallium nitride (GaN), aluminum nitride (AlN), silicon carbide, zinc oxide, silicon (Si), and glass. For example, preferred substrates are (0001) zinc oxide, (111) Si, (111) GaAs, (0001) GaN, (0001) AlN, (0001) sapphire, (11-20) sapphire, and (0001) silicon carbide. possible.

  The substrate for the device of the present invention can be prepared for semiconductor layer growth by chemically cleaning the grown surface. The growth surface of the substrate may optionally be polished. The substrate may also be heated and degassed prior to layer growth. The surface of the substrate can optionally be nitrided as disclosed in US Pat. No. 6,953,703, incorporated herein by reference. Growth on an unpolished, untreated substrate in a cut state facilitates growing a textured surface thereon.

  The semiconductor layer can be formed by several processes, such as hydrogenated vapor deposition (HVPE), metalorganic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE), liquid phase epitaxy (LPE), laser ablation and It can be grown by variations of these methods. Exemplary growth processes are disclosed in US Pat. Nos. 5,725,674, 6,123,768, 5,847,397 and 5,385,862, incorporated herein by reference. Yes. The semiconductor layer can also be grown in the presence of nitrogen resulting in a nitride layer. Examples of nitride layers include GaN, InN, AlN, and alloys thereof.

  FIG. 1 is a partial representation of a semiconductor device of the present invention. In a preferred embodiment, the apparatus comprises a textured substrate 2 and a first layer 4 that is textured when grown thereon. The substrate 2 is initially textured or can be polished smoothly. The first layer 4 is textured when grown on the substrate 2 and has a textured surface topology 10. The first layer is preferably grown by a modified HVPE deposition process to produce a textured surface 10. The modified HVPE process partially produces a first layer that is textured as it is grown by etching the defective areas of the layer with an enhanced hydrochloric acid (HCl) concentration. The HCl concentration of the modified HVPE process is substantially higher than that of a typical deposition process, as illustrated below.

  In one embodiment, the first layer 4 may be a semiconductor layer composed of a group III nitride layer. This layer 4 is preferably a semiconductor layer that has been made p-type or n-type by suitable doping during deposition, as shown below, but it may also be an insulating layer such as AlN, or both. . Layer 4 can optionally be grown on a buffer layer deposited on a substrate, as described in US Pat. No. 5,686,738, incorporated herein by reference.

  The thicknesses of the substrate 2 and the layer 4 can cover a wide range, but the thickness of the layer 4 affects the degree of the textured reproduction on the surface. For example, a 100 μm thick layer can have a peak-to-valley texture distance of about 100 nm to 5 μm. The texturing of the semiconductor layer affects the light extraction characteristics of the LED layer that is grown on the layer and replicates the texture. The semiconductor layer 4 is typically textured randomly during growth. The layer 4 is a single crystal or polycrystalline material.

  FIG. 2a shows a second layer 8 grown on the device of FIG. This layer 8 is grown by any suitable deposition process. The second layer is grown on the textured surface 10 of the first layer 4. The second layer 8 is preferably not thick enough to embed the textured surface topology 10 of the first layer 4 as shown in FIG. 2b. The second layer 8 preferably has a top surface 9 that is textured by duplication with the layer 4, as shown in FIG. 2a.

  The layer 8 is preferably a semiconductor layer made of group III nitride. The second layer 8 is typically a p- or n-type semiconductor layer opposite to the doping of the layer 4. The second layer 8 is a single crystal or polycrystalline semiconductor layer. In one embodiment, the doping of the first and second layers 4 and 8 forms a pn junction 3 that is used as a photosensor or emitter. These devices can be used for electronic displays, solid state lights, computers or solar panels. Electrodes 11 and 13 are connected to layers 4 and 8 as is known for such applications in the art.

  3a and 3b are partial representations of an LED having multiple quantum wells 6 grown on the device of FIG. The quantum well 6 is textured by the surface topology of the first layer 4. As described above, the first layer 4 can be textured when grown on the substrate 2. In one embodiment, the multiple quantum well 6 comprises one or more barrier layers 5 and quantum well layers 7 alternately.

  Several barrier layers 5 and quantum well layers 7 can be grown by alternating semiconductor layers each replicating the textured first layer 4. For example, the quantum well can be formed by a barrier layer 5 grown on the first layer 4. The quantum well layer 7 is then grown on the barrier layer 5. Then, the second barrier layer 5 is grown on the quantum well layer 7, on which the second quantum well layer is grown. In one embodiment, the quantum well layer 7 and the first layer 4 are matched in composition. The barrier layer 5 can have a composition different from both the first layer 4 and the quantum well layer 7.

  The barrier layer 5 can comprise one or more III-V nitride compounds. In one embodiment, the one or more barrier layers 5 are AlGaN. Similarly, the one or more quantum well layers 7 are group III nitrides, such as GaN, or another group III-V compound. These layers are also grown by any suitable deposition process. These layers are monocrystalline or polycrystalline layers.

  The thickness of each layer is typically thin enough to texture the underlying layer and replicate the surface. The degree of texturing for these layers affects internal quantum efficiency (IQE) and light extraction efficiency. The device of the present invention preferably comprises 1 to 20 quantum wells and constitutes a plurality of barrier layers 5 and quantum well layers 7.

  FIGS. 3 a and 3 b also show the upper semiconductor layer 8 grown on the textured multiple quantum well 6. This layer 8 can be grown by known deposition processes. This layer can be textured layer 9 (FIG. 3a), thick enough to embed the textured surface topology of the first layer 4 (FIG. 3b), or it can be polished. is there.

  The layer 8 is preferably a semiconductor layer made of group III nitride. The upper layer 8 is also a p-type or n-type semiconductor layer opposite to the layer 4 and forms a pn junction. This pn junction makes it possible to function as a semiconductor device, for example an LED or a photodetector. The upper layer 8 is a single crystal or polycrystalline semiconductor layer. The multiple quantum well 6 can also comprise a barrier layer 5 and a quantum well layer 7 that are textured during growth. For example, layers 5 and 7 can be grown by a deposition process such as HVPE, MBE, or MOCVD.

  The device structure shown in FIG. 3a can exhibit an internal quantum efficiency and an external light extraction efficiency that are significantly higher than those of conventional devices. The device of FIG. 3b has an overall increase in internal quantum efficiency (IQE).

  The device of the present invention can have a light extraction efficiency close to 100%. Similarly, such a device may have an internal quantum efficiency (IQE) in the range of 50-60% or more.

  Figures 4a and 4b show a device with a substrate having an initially textured surface. The layer following the first layer 4 is deposited on the textured substrate 2 and the upper surface is textured by replication.

  The device of FIG. 4a comprises a textured surface 9 on the layer 8 or, in FIG. 4b, an untextured layer in that embodiment.

  In an alternative embodiment, the substrate has both textured upper and lower surfaces 9 and 15 as shown, for example in FIG. 5a, using substantially the same procedure as described above. In FIG. 5b, only the bottom layer 2 is provided, the surface 15 is textured and can function as an emission surface.

  For example, FIG. 5 c is an LED using a flat AlN template 4 a on the sapphire substrate 2. Between the AlN template and the quantum well and barrier layers 7 and 5 is a thick AlGaN layer 4b known as a cladding or contact layer. This layer may be used with other forms of the invention described herein. Above them are p-doped layers 8a and 8b of AlGaN and GaN, respectively. The layers 4 b and 8 b receive the electrical connectors 11 and 13 and perform light extraction downward through the sapphire substrate 2. Layer 8a is used with other forms of the invention described herein and functions as an electron blocking layer to prevent loss of electrons. Layers 5 and 7 are shown flat for clarity, but should be understood to be crimped as desired.

  The present invention also provides a method for fabricating the semiconductor device of the present invention. The method includes providing a substrate and growing a first semiconductor layer on the surface of the substrate. The first layer is randomly textured during growth, textured with a slab after growth, or textured with a randomly textured substrate surface, as described below. The substrate or first layer can then be used as a template to deposit and texture other semiconductor layers. Such templates are sold at this manufacturing stage, allowing others to complete the multi-layering and replicate the texture to the release layer.

  In a preferred embodiment, the fabrication method comprises growing several quantum wells. In this case, the well includes both a barrier and a quantum well layer that can be deposited with alternating semiconductor layers. The multiple quantum well is textured by the first layer, the substrate, or a combination thereof.

The present invention describes a method of forming thick GaN and other III nitride films (templates) with special textures on a substrate. The textured nitride template thus formed spontaneously is used as a substrate for the development of high efficiency devices such as III nitride light emitting diodes (LED), solar cells and photodetectors. The high efficiency of such a device is due to two effects.
(A) Effective light extraction for LEDs, and effective coupling of light into the material for solar cells and photodetectors.
(B) Improvement in IQE of LEDs based on textured III-nitride MQW by suppressing polarity effect.

  The present invention relates to a method for preparing a textured III-nitride template during growth of nitride films by HVPE, MOCVD, and MBE. Also, such textured nitride templates are used as substrates for the growth and fabrication of LED structures with improved IQE as well as more effective extraction efficiency. Furthermore, other devices such as LEDs, solar cells and photodetectors made on such textured templates will also have improved efficiency. Commonly owned US Pat. Nos. 5,385,862, 5,633,192, 5,686,738, 6,123,768, 5,725,674 are hereby incorporated by reference.

Where the internal efficiency of the LED is an inherent material and device design characteristic, the external efficiency of such a device is a measure of the light extraction efficiency from the semiconductor. The large difference between the GaN index of refraction and the surrounding material (usually air) results in total internal reflection for most of the light generated in the active material. For the refractive index of GaN (n = 2.5), the conical shape through which internal light leaks is limited by Snell's law within the critical angle of sin θ = 1 / n, or θ = 23.5 °. It limits the total amount of radiation extracted for a solid angle.
Ω = 2Π (1-cosθ)

Here, the total fraction of light that can leak from the semiconductor can be calculated by dividing the previous equation by 4Π.
Ω / 4Π = 1/2 (1-cosθ)
This formula extracts only 4% of the incident radiation into the GaN based LED. Here, in the LED, most of the internally reflected radiation is reabsorbed, because this is in the LED that operates below the threshold for emitting a laser beam, and the purpose stimulation gain is less than the purpose absorption loss. Few.

  The formation of the III nitride template and the epitaxial growth of the nitride device on such a template is effected using three different epitaxial methods, for example as described below.

  The HVPE method is used for the development of GaN or AlN apparent substrates (templates). This deposition method uses HCl to transfer Ga to the substrate in the form of GaCl. The growth of GaN in the presence of HCl also has many additional advantages. HCl etches excess Ga from the surface of the growth film, and this allows for high growth rates (100-200-μ / hr). It also etches initially defective GaN at the hexagonal domain boundaries due to incomplete coalescence of such regions. After all, another advantage is the scavenging of metal impurities, which helps to contribute to recombination centers in most semiconductors. Thus, this method results in a very high quality GaN film.

The GaN template textured according to the invention is grown by a modified HVPE process. This GaN template can be grown through a modified HVPE reactor. Within this reactor, the group III precursor can be GaCl gas, which is synthesized upstream at a temperature of about 500 ° C. to 1000 ° C. by HCl flowing over a quartz boat containing Ga. The GaCl gas is then mixed with ammonia (NH ₃ ) near the surface of the downstream substrate wafer to form GaN at a temperature of about 900 ° C. to 1200 ° C. The GaN or AlN or AlGaN template of this invention can be grown along polar and non-polar directions. Templates can also be grown in their cubic structure by selecting substrates with cubic symmetry, such as (100) Si or (001) GaAs. In this case, the subsequent nitride layer grown thereon also has cubic symmetry.

The deformation reactor is generally divided into four zones, and the temperature of each zone can be individually controlled. The reactor also has three separate delivery tubes for the reactant gas and diluent. Nitrogen and hydrogen are used as diluents and carrier gases for NH ₃ and HCl. Nitrogen is routed through an intermediate tube that acts as a downstream gas sheath to prevent GaCl and NH ₃ gas from being mixed before contacting the substrate surface. The texturing of the GaN layer can be the result of the etching effect of HCl. For example, texturing occurs when HCl etches Ga from the surface of the growing layer. HCl also etches defective GaN in the boundary domain of the first layer. The HCl concentration of the modified HVPE process is substantially higher than that of a typical deposition process where texturing is avoided.

The textured GaN template can be grown under high growth rate conditions in the range of about 30-200 μm per hour controlled by the flow rate of NH ₃ relative to the group III precursor. This flow rate is typically about 300-10. Template growth can be done by pre-treating the substrate with GaCl gas or by exposing the sapphire surface to 1000 ° C. for a short time (nitrided) ammonia and then growing a thin GaN buffer layer at 550 ° C. to 650 ° C. Done. The growth region is then graded to about 1070 ° C. for high temperature epilayer growth of GaN. The substrate can also be pretreated prior to growth with sputtered zinc oxide. The typical thickness of zinc oxide is about 500-1500. The template is then grown by heating the chamber to the growth temperature and flowing a reaction gas to initiate further growth.

MOCVD is a recently used method by the industry for the growth of GaN based LEDs. This method produces a nitride by reaction of NH ₃ with a group III alkyl (eg, (CH ₃ ) ₃ Ga or (C ₂ H ₅ ) ₃ Ga). One problem with this method is the cost due to the high consumption of NH ₃ . Growth of GaN film at 1 μ / hour requires 5-10 lpm (= liter / min) of NH ₃ .

  The MBE method forms III nitrides by reaction of activated molecular nitrogen with group III elements by various formations of RF or microwave plasma. Another approach to take is the reaction of ammonia and group III elements on a heated substrate. Group III elements are either evaporated from the effluent cell or supplied in group III alkyl form. It is generally believed that the products produced by the MBE process are more expensive due to throughput yield issues. However, in nitride growth, an important part of the cost is determined by consumption of the nitrogen precursor. During MBE growth of nitride devices, nitrogen or ammonia near 1-50 sccm (standard cc / min) is used, which is several orders of magnitude lower than that used during MOCVD growth. This and the fact that MBE manufacturing equipment uses a multi-wafer deposition system makes the MBE process attractive for the development of inexpensive nitride equipment. Laser diodes based on InGaN have recently been manufactured by the MBE method. (Hooper, Electronics Letters, Volume 40, January 8, 2004)

One aspect of the present invention is that the surface of the GaN template is randomly textured. A suitable random surface texture can be produced by several suitable mechanical or chemical techniques including modified HVPE. In the modified HVPE, the surface texture of the GaN template can be controlled by changing the ratio of group III to group V. For example, using a molar ratio of NH _{3 to} HCl of 5: 1 to 10: 1 results in randomly textured GaN templates with modified HVPE, whereas 20: 1 to 50: 1 or more Using a high ratio, conventional HVPE produces a flat template. Other methods for producing randomly textured GaN include incomplete nitridation of the substrate, such as a sapphire wafer, or using a very thin GaN buffer. Growth of GaN at high temperature under nitrogen-rich conditions also results in randomly textured GaN templates by MBE method. For example, using a Ga / N molecular ratio of 1 or less results in a randomly textured GaN template. Using a molecular ratio of one or more Ga / N results in a flat GaN template.

  Surface texture can be studied using available techniques such as atomic force microscopy (AFM) and scanning electron microscopy (SEM). The degree of randomness can be determined by determining the surface depth distribution, and the randomly textured surface approximately exhibits a Gaussian distribution of surface depth. In order to obtain optimum light extraction from the emitter, the average surface depth is preferably within the wavelength range of the emitted light. For example, for visible light LEDs, an average surface depth in the range of 200 nm to 1.5 μm is preferred.

  Textured III-nitride templates can be formed along polar or non-polar directions.

  Most of the work in III-nitrides reported in the literature involves heteroepitaxial growth of these materials on (0001) sapphire or 6H-SiC substrates by various deposition methods. Materials and devices grown on these substrates contain a high density of threading defects (dislocations and transition domain boundaries). Furthermore, the (0001) orientation is the polarity direction of the non-centrosymmetric wurtzite structure, which creates an internal electric field in the heterostructure due to spontaneous and piezoelectron polarities. If such polar effects may be desired for some device types (eg, piezoelectron doping in FETs), they may not be desirable for emitters based on QCSE multiple quantum well (MQW) structures. This effect results in a red shift in QW radiation due to quantum well distortion, and also results in reduced quantum efficiency because the electron and hole wavefunctions are separated in space.

  It has recently been demonstrated that the growth of GaN / AlGaN MQWs on R-plane sapphire (10-12) leads to films along the (11-20) direction (Ayer et al., 2003). The (11-20) direction has a polarity vector in the plane of the MQW, which removes the internal field perpendicular to the quantum well. Therefore, radiation from such quantum wells does not shift red and luminescence efficiency does not decrease.

  Textured nitride templates along the polar direction can be grown on (0001) sapphire, (11-20) sapphire, 6H-SiC, (0001) ZnO, (111) Si, (111) GaAs. Textured nitride templates along non-polar directions can be grown on R-plane (10-12) and M-plane (10-10) sapphire substrates and corresponding planes of 6H-SiC and ZnO. Such a textured template can be grown by three deposition methods as previously discussed.

  The textured nitride template is used as a substrate for the growth of high efficiency LEDs. Due to the effect that the surface is spontaneously textured to some extent during growth, the gradual change of the refractive index from the bulk of the semiconductor into the air effectively increases the light leakage cone, and the light is transmitted via internal reflection. Reduce losses. Thus, the light emitted from the semiconductor is extracted more efficiently, thereby increasing the external quantum efficiency of the device. In similar discussion, photodetectors and solar cells grown on such templates will absorb light with higher efficiency, and they do not require further anti-reflective coatings.

  Furthermore, the textured nitride surface can also increase the IQE of LEDs based on III-nitride semiconductor MQWs due to partial suppression of the polar effect.

  GaN templates can be grown by HVPE method with various surface textures. These templates are characterized by their surface morphology, reflectivity, migration and photoluminescence properties. The luminescence extraction efficiency can be almost 100%. GaN / AlGaN MQW can be grown on flat and textured GaN templates. Since QW is not perpendicular to the (0001) polarity direction, the photoluminescence dimension on the pleated QW is a significant improvement in IQE and a reduction in the quantum limit Stark effect (QCSE) compared to that from flat QW. The resulting results are shown. Nitride LED structures that incorporate pleated QWs have significantly higher external quantum efficiencies than those using flat quantum wells.

  The textured boundary between the GaN layer (top layer) and air (or other material) increases extraction efficiency with respect to photon trajectories across the boundary by reducing the amount of total internal reflection within the top layer . The surface features of the textured surface can have characteristic features as small as about one wavelength. However, larger texture features are acceptable. The top layer can grow more conformally on the lower layer, like a textured template. The top layer can be thousands of inches thick, but is not necessary.

  The boundary between the GaN layer and air (or other material) is textured on a template, eg n-type GaN layer, interference layer, eg quantum wells (QWs) or MQWs, which are textured Although grown or deposited conformally on the template, it can be textured by growing and depositing a GaN layer directly on them. As an alternative, even if the GaN layer does not grow on the textured surface, a flat GsN layer can be grown and subsequently the surface can be roughened, for example by lithography. Thus, roughening after growth can impair the surface of the GaN layer. For example, a “point defect” may occur. However, this obstacle can be corrected, for example, by annealing.

  The MQW can be grown on the n-GaN layer before the p-GaN layer is grown on the MQW. For example, the MQW layer can be grown by MBE or MOCVD. In one embodiment, 10 pairs of GaN wells and AlGaN barriers are grown with each well and each barrier having a thickness of about 78 mm. In another embodiment, each layer is 50 inches. However, a wide range of well and barrier thicknesses (including 50 mm or less, including 78 mm or more) are acceptable. The overall thickness of MQW can be 1000 mm or more. Furthermore, the well and barrier layers need not be the same thickness. For example, a 70 Å (each) well layer can be combined with an 80 障壁 barrier layer.

  As mentioned, textured MQW between n-type and p-type GaN layers increases the IQE of the pn junction, thereby increasing the amount of light produced by the pn junction (or in the case of photodetectors). Increasing the amount of external light detected at the junction). Embodiments can include textured joints only, textured top layer only, or a combination of textured joints and textured top layer. Furthermore, any of these embodiments can include textured QWs or MQWs, or alternatively can be deleted.

  A textured pn junction (with or without QWs or MQWS) gives a constant radius or other outer dimension of the LED or other semiconductor device surface (contact) at a larger junction than a flat pn junction It has an area. This increased surface area can increase the efficiency of the device.

  To record a lithographic mask or the like on an integrated circuit wafer, for example, for processing steps involving subsequent wafers, when a light source illuminates the wafer through a microscope, an operator typically observes the wafer through the microscope. The light illuminates the top surface of the wafer, creating a record mark on the wafer that is visible to the operator. However, small amounts of light are reflected from devices that include one or more of the characteristics described above. Thus, it can be difficult to observe a recording mark on the surface of a wafer constructed according to one or more aspects of the present invention using an optical microscope. This difficulty of observation can lead to the difficulty of recording lithographic masks used in subsequent processing steps. To overcome this difficulty, according to another embodiment of the present invention, the light source illuminates the edge (side) of the wafer, thereby creating a recording mark on the wafer that is visible to the operator. Rather than being reflected off the surface as in the prior art, the light is transmitted from the surface of the wafer through the microscope to the operator. The light source can be external to the microscope but is not necessary.

  The present invention also provides a new type of white LED. A textured InGaN / GaN MQW based LED grown on a textured GaN template manufactured by HVPE produces two-color electroluminescence and generates white light. For example, the color temperature of a white LED according to the present invention ranges from about 2500 ° K to about 7500 ° K, and can be varied by changing the DC injection current. The first peak of electroluminescence is typically in the range of about 390-450 nm and the second peak is in the range of about 500-600 nm. The color of the combined dichroic radiation depends on the bias or injection current used to drive the electroluminescence. The overall color is a blue shift with increasing injection current, with the overall contribution increasing from a peak in the range of 390-450 nm. The dichroic emission of the LED according to the invention is believed to result from the emission of light from two or more different regions of the randomly textured MQW. Since the deposition process produces somewhat thick wells in the flat region and somewhat thin wells in the graded region, the quantum wells in the randomly textured MQW have at least two different thicknesses. Thinner wells emit higher energy, which results in emission peaks that are blue-shifted compared to thicker well layers.

  In one embodiment, an LED according to the present invention is combined with one or more conventional LEDs, resulting in a modified or all spectrally coupled LED device. In another embodiment, two or more LEDs according to the present invention each have different electroluminescent properties, such as, for example, a coloring temperature, but combine to produce a changed or all spectrally coupled LED device.

  In addition to the bias current effect in LED coloring, the overall electroluminescence spectrum of the LED of the present invention can be altered by changing the In content. In may be present in an amount varying from at least 10% to 100% of a given III nitride layer of the device. Increasing the In content results in a red shift of the electroluminescence spectrum.

  The color changeable feature of the LED according to the present invention has many applications, such as a color changeable indicator and display device, a still picture or photograph, a colored image display for displaying a video image, and a projection device for a still image or video. Including use in the production of Techniques and apparatus for the placement and control of LEDs according to the present invention for manufacturing colored image displays are well known in the art. For example, a conventional digital driver for an LED image display is disclosed in US Pat. No. 7,109,957, but is shown here for reference. Such control devices can be modified to control the bias current of the LEDs of the present invention to modify their color to form a colored image. Similarly, techniques including optics for making projection devices using control circuitry, software, and LED arrangements are well known and can be adapted for use with LEDs according to the present invention. For example, U.S. Pat. No. 6,224,216 describes such an LED projector and is referred to in its entirety.

  The examples herein are given to illustrate the advantages of the present invention. These examples may include or incorporate any of the variations or embodiments of the invention described above. The embodiments described above can also include or incorporate any or all of the other embodiments of the invention. The following examples are not intended in any way to limit the scope of the invention.

Growth of textured GaN templates by HVPE Textured GaN templates are produced by the modified HVPE process described above. FIG. 7 shows an electrically excited wafer level LED emitting at the p-contact 20. This blue LED structure was made on an unpolished (0001) sapphire substrate. On this substrate, a heavily doped n-type GaN of 3 microns was grown, and then 10 MQWs with InGaN containing 13% indium as well and GaN as a barrier were grown. Following the growth of MQW, a thin (about 10 μm) electron blocking layer of AlGaN containing 30% Al, doped p-type with magnesium, is then grown and then heavily doped p-type with magnesium at 200 nm GaN is grown. The free surface from which light is emitted replicates the morphology of the unpolished sapphire substrate.

  FIG. 8a shows a scanning electron microscope (SEM) image of a randomly textured GaN template when grown by a modified HVPE process. This image was captured for a sample tilted about 30 degrees with respect to the electron beam. The growth of the GaN layer occurred on the (0001) sapphire substrate. This growth was performed during the 1000 ° pretreatment by a process using 25 standard cubic centimeters per minute (sccm) of HCl. This process also used an ammonia to group III ratio of 150 during buffer layer growth at about 590 °. The high temperature growth stage at 1070 ° then used a ratio of ammonia to group III of 60. The degree or degree of template texture determination was determined to depend on the amount of GaCl that reached the growth front. Such an amount of GaCl can also control the growth rate.

  Compared to FIG. 8a, FIG. 8b shows an SEM image of an atomically flat standard GaN layer. As shown, the surface topology of the normal GaN layer is not textured despite a few surface defects. This image was captured for a sample tilted about 30 degrees with respect to the electron beam. The photoluminescence of a conventional GaN layer with an atomically flat surface was compared to that of the randomly textured gallium nitride template of the present invention. Both layer samples were measured under identical conditions using a 10 milliwatt (mW) helium cadmium laser as the excitation source.

  The result of this comparison is illustrated by FIG. In this figure, the photoluminescence intensity of the textured template is more than 50 times greater than the intensity of the flat GaN layer. Enhanced light extraction occurs through surfaces that are specifically textured by the high refractive index of such semiconductor layers. The textured surface increases the escape cone of single photons compared to the escape cone limited by the high refractive index change between the GaN layer and air.

  The randomness of texturing of the Group III layer template of the present invention is depicted in FIGS. 10a and 10b. FIG. 10a is an atomic force microscope image of the GaN template of the present invention with the depth analysis plot of the imaging region of FIG. 10b. This plot shows the Gaussian distribution of surface topology, randomness characteristics for the template. The average peak-valley surface topology is about 1.3 microns.

Growth of composite pleated quantum wells on textured template FIG. 6 is a transmission electron microscope image showing multiple quantum wells (folded quantum wells) on a textured surface. These quantum wells comprise 10 pairs of AlGaN and GaN layers. Individual GaN layers may consist of textured quantum well layers. In this case, the AlGaN layer acts as a barrier layer. The composition of the AlGaN layer is, for example, Al _0.2 Ga _0.8 N. Generally, it is Al _x Ga _1-x N. Multiple quantum wells can also be made by any combination of small gap III-V nitride films (wells) and large gap III-V nitride films (barriers). The composition of MQW determines the light emission energy from about 0.7 eV of pure InN to 6 eV of pure AlN. The plurality of quantum well layers are grown by any suitable deposition process. The MBE process involves the reaction of a group III material to nitrogen that is activated by radio frequency or microwave plasma. An alternative solution is to react the group III material with ammonia on the heated substrate.

  Group III materials for semiconductor growth by growth processes can be evaporated from the effusion cell or can be provided in the form of Group III alkyls. During semiconductor growth in MBE processes or plasma assisted MBE processes, nitrogen and ammonia gases are typically used at about 1-100 sccm. When the quantum well is grown, the quantum well layer replicates the texture of the template. Such MBE processes are known in the art. The present invention also contemplates other typical semiconductor growth solutions that may be used by those skilled in the art.

  Ten pairs of textured AlGaN and GaN quantum wells had a well thickness of about 7 nanometers (nm) and a corresponding barrier layer thickness of about 8 nm. A plurality of quantum wells were grown on the substrate at a temperature of about 750 °. First, an AlGaN barrier layer is grown on the textured Group III template of the present invention. The barrier layer then becomes the deposition surface for the quantum well and GaN layer. The GaN layer then becomes the growth surface for the next barrier layer. This growth pattern can be continued until a multiple quantum well layer is formed. These wells replicate the surface topology of the underlying textured template. The thickness of the well and barrier layer can be, for example, 10 to 500 mm or more.

  Figures 11 and 12 show the photoluminescence spectrum of a conventional quantum well and the textured quantum well grown on the textured template of the present invention, respectively. The photoluminescence spectrum from a quantum well grown on a normal flat GaN layer exhibits a high intensity peak at 364 nm. This intensity peak is primarily attributed to a flat bulk GaN layer directly under the MQW. The very low and broad luminescence peak at about 396 nm is assumed to be due to a flat well. The cathodoluminescence spectrum of a flat well sample was used to verify this assumption. This spectrum was performed using a low acceleration voltage of about 4 kV to search for quantum wells. These results are shown by the inset in FIG. These results confirm that the broad peak produced at about 396 nm corresponds to a normal quantum well.

  Therefore, the luminescence observed from flat quantum wells is shown as being greatly reduced in size and red-shifted relative to the bulk. These results are consistent with the quantum confined Stark effect (QCSE).

  Compared to a typical quantum well, the photoluminescence spectrum of the quantum well textured by the textured template of the present invention is blue shifted with respect to the luminescence spectrum of the bulk GaN layer. The plurality of textured quantum wells exhibit a substantially increased luminescence when compared to the template on which the well is grown.

  These results indicate that the pleated well formed on the textured III-nitride template is not distorted by the internal electric field associated with polarization. FIG. 12 also shows that the peak photoluminescence for the textured quantum well is about 700 times higher than that grown on a regular flat GaN layer. This difference is due to both enhanced light extraction through the textured surface and the spontaneous emission rate enhanced by QCSE elimination.

Textured Surface Created by Etching Masked Template In this example, the textured substrate is made with a textured surface. On this surface, additional layers are grown while replicating the textured features. The additional layer is grown to form the textured template, pn junction or optical device of the present invention. The additional layer can also comprise a multiple quantum well formed by a plurality of wells and barrier layers. The surface of the substrate to be textured is flat or textured in advance. The surface of the substrate is also unmodified or otherwise left natural.

A mask structure comprising a monolayer of monodispersed spherical colloid-like particles is coated on the surface of the substrate. This substrate is silicon, silicon carbide, sapphire, gallium arsenide, gallium nitride, aluminum nitride, zinc oxide or glass. Spherical monodispersed colloidal particles are commercially available in sizes ranging from 0.02 to 10 microns. The packing of the particles onto the surface of the substrate is either periodic or random, depending on the technique used for coating. Covering the 1-5 inch diameter portion of the substrate with the mask structure takes several minutes. Such a coated area can define features of 10 ⁸ to 10 ¹² submicron on the substrate.

  The masked surface is then etched, for example by ion beam etching. This etching turns individual particles into pillars on the substrate surface. The aspect ratio and shape of the pillar are determined by the relative mask etch rate and the underlying substrate material. Both physical and chemically assisted ion beam etching can be used to minimize pillar aspect ratio. The surface of the substrate is then etched with a liquid or gas such as hydrogen fluoride, chlorine, boron trichloride or argon. Etching the substrate with liquid or gas is less significant in some areas than in other areas. This is because pillars tend to delay or prevent etching of portions of the substrate surface.

  After etching, the pillars on the surface of the substrate are removed with a solvent. This solvent dissolves the pillars and creates a textured surface on the substrate. The surface of the substrate is then used to grow additional layers that replicate the textured features. This technique for etching and texturing the surface of a substrate is described by Deckman et al., “Molecular Scale Microporous Superlattices”, MRS Bulletin, pp. 24-26 (1987).

Fabrication and characterization of LED structures on textured GaN templates
LED structures were fabricated on HVPE growth templates with different textures. The device structure is shown graphically in FIG. An 800 μ × 800 μ mesa was formed by ICP etching. Metal contacts are deposited by light evaporation, n-GaN is Ti (10 nm) / Al (120 nm) / Ni (20 nm) / Au (80 nm) and p-GaN is Ni (5 nm) / Au (20 nm) It was done. The Au metal at the top of the mesa was quite thick and only a small amount of light generated in the LED structure was transmitted. The spectral dependence of two devices with different surface textures is shown as a function of injection current in FIG. These data show that due to the increase in injection current, the illuminating light occupied the entire region of the visible spectrum, resulting in white light. According to the visual inspection of luminescence, it is observed that blue and green luminescence arises from different parts of the mesa. This is evidence that the broad green spectrum is not related to defects, but the radiation from the plane QW is approximately perpendicular to the polar direction. This emission is red-shifted by QCSE. This interpretation is consistent with a second LED with a flatter surface.

Fabrication of thick n-GaN template by HVPE method on c-plane sapphire substrate The growth conditions of this method are n- with various degrees of surface morphology from atomically flat to completely random texture. Tuned to lead to type GaN template. These GaN templates were characterized by studying their reflectivity in the UV and visible parts of the spectrum as well as their photoluminescence (PL) excited with a He-Cd laser. The reflectivity was suppressed from about 20% of the flat surface to 1-2% of the randomly textured surface in the entire spectral region. It has been discovered that the intensity of photoluminescence from a textured GaN template is significantly higher than that from a similarly manufactured and similarly doped GaN template with an atomically flat surface. In particular, the ratio of integrated photoluminescence between the GaN textured template and the GaN template with a flat surface was about 55, measured under the same conditions. The significant increase in photoluminescence from randomly textured GaN templates is due in part to increased light extraction through the textured surface, which can only be expected to be 4% from a flat surface, It is also due in part to an increase in spontaneous emission due to exciton localization on the textured surface.

  The same GaN / AlGaN MQW with 7 nm well and barrier width is grown on both textured and flat GaN templates textured by plasma assisted MBE, and their optical properties are photoluminescence (PL) and cathode Evaluated by luminescence (CL) measurement. The photoluminescence spectra of flat and pleated QWs showed significant differences. The photoluminescence from the flat quantum well has a single peak at 396 nm, consistent with the red shift expected from the photoluminescence spectrum of the bulk GaN film by QCSE. The photoluminescence peak from the pleated QW produced at 358 nm is blue shifted with respect to the photoluminescence spectrum of the bulk GaN film, and the result is consistent with a QW having a square shape. Furthermore, the integrated photoluminescence intensity from multi-pleated quantum wells is about 700 times higher than that of flat MQW.

  The significant increase in photoluminescence from pleated QW is due in part to an increase in light extraction through the textured surface and an increased spontaneous emission rate. Since quantum wells are not perpendicular to the polar (0001) direction, it is believed that the increase in IQE is due to a decrease in QCSE. Further increases in IQE are believed to be due to quantum carrier limitations from the wedge-shaped electron intrinsic mode. The latter originates from a transition in carrier behavior from 2D to 1D due to the V-shaped intersecting plane of the quantum well, where the wedge shape behaves as a quantum string, which results in exciton localization and trapping.

Formation of textured surface of III nitride along the polar (0001) direction
GaN textured template was prepared by HVPE method. The GaN textured template was grown in a custom made HVPE reactor (see FIG. 20). In this reactor, the Group III precursor, GaCl (g), was synthesized upstream by flowing hydrochloric acid (HCl) over a quartz boat containing Ga at a temperature between 500 ° C. and 1000 ° C. GaCl is mixed with ammonia (NH ₃ ) near the surface of the sapphire wafer to form GaN at a temperature of 900 ° C. to 1200 ° C. as shown in FIG. The reactor was divided into four zones, and the temperature in each zone was individually controlled. It had three separate discharge tubes for reaction gas and diluent. Nitrogen and / or hydrogen were used as diluent and carrier gas for both NH ₃ and HCl. Nitrogen, Nitrogen for GaCl and NH ₃ is prevented from mixing before before impinging on the substrate surface was also sent through the central tube, which acts as a gas curtain or sheath downstream.

GaN templates (both flat and with randomly textured surfaces) have high growth rate states in the range of 30-200 μm / hour controlled by NH ₃ / III precursor flow ratios of 10 to 300 Grown under. Templates were grown using a variety of techniques. One of these was a three-step growth method using substrate surface pretreatment using GaCl (g) or nitridation of a sapphire substrate at 1000 ° C., followed by growth of a thin GaN buffer layer at 590 ° C. Also, the growth zone was raised to 1070 ° C. for high temperature GaN growth. Another method used external pretreatment of the sapphire surface prior to growth with sputtered ZnO. The usual thickness of ZnO was 500 to 1500 mm. The growth of the GaN template is performed by directly heating the chamber to the growth temperature and flowing a reaction gas to start the growth.

FIG. 8a shows an SEM image of a GaN template with a random texture grown by the HVPE method. Growth is in three stages using 25 sccm HCl during pretreatment at 1000 ° C., NH ₃ / III ratio of 150 during buffer layer growth at 590 ° C. and NH ₃ / III ratio of 60 during high temperature growth at 1070 ° C. This is done using growth technology. The degree of texture was observed to depend on the amount of GaCl reaching the growth front that also controls the growth rate.

  The reflectivity of the textured surface described in FIG. 8a is shown in FIG. As can be seen from this drawing, the reflectivity was less than 1% between 325 nm and 700 nm. This should be contrasted with a flat film reflectivity of about 18%.

  Room temperature photoluminescence (PL) from two GaN films grown by HVPE, one with an atomically flat surface and the other with a randomly textured surface, is shown in FIG. The two films were measured under the same conditions using a 10 mW HeCd laser. From these data, we see that the photoluminescence intensity of the sample with the textured surface was 55 times greater than the photoluminescence intensity of the flat film.

Photoluminescence of GaN templates with different surface roughness GaN templates with different surface textures are grown and their photoluminescence spectra are measured using an argon-ion laser emitting at 244 nm with an output of 20 mW It was. These templates are first characterized by atomic force microscopy (AFM). FIGS. 25-32 show the AFM surface morphology for the GaN textured templates VH092403-81 (VH81), VH082504-129 (129), VH061603-63 (VH63) and VH080604-119 (VH119). The rms roughness of these templates is variable from 627 nm to 238 nm. Other information from these data is listed in the drawing legend.

  The photoluminescence spectrum for the GaN textured template described in FIGS. 25-32 is shown in FIG. The insets listed are the rms roughness of various templates with full width at half maximum (FWHM).

  The peak intensity versus rms roughness is shown in FIG. It is clear from these data that the luminescence intensity increases with rms roughness.

  To further test the efficiency of the GaN textured template in light extraction, excitation intensity dependent photoluminescence measurements were made. Figure 22b shows the measurements made with a flat film with the same carrier concentration and a textured template, whereas Figure 22a shows several with different degrees of texturing, including GaN with a flat surface. A comparison of the efficiency between templates is shown. From the drawing it is clear that high photoluminescence intensity is not due to high n-doping.

Formation of III-nitride surface along non-polar direction FIG. 23 shows the type of surface texture obtained with GaN film grown on R-plane sapphire (1-102) by HVPE. This template is also grown by a three-step process as described in Example 7.

  The reflectance of the textured surface described in FIG. 23 is shown in FIG. As can be seen from this figure, the reflectivity was 1% or less between 325 nm and 700 nm.

Formation of GaN / AlGaN multiple quantum wells (MQWs) on textured GaN templates along the polar direction To further test the ability to form LED structures on textured GaN templates, 10 pairs of GaN / A template with GaN textured Al0.2Ga0.8N MQWs was deposited on VH129 by MBE (see FIG. 28). MQWs were formed using RF plasma source to activate nude nitrogen efflux cell evaporating molecular nitrogen and Ga and Al. Various MQWs were formed by Si introduced into either quantum wells or barriers, or both, and were doped n-type. Alternatively, MQWs could be grown using NH ₃ as the nitrogen source. Similar MQW structures could also be grown by MOCVD. Similar methods could also be used to grow InGaN / AlGaN MQWs with different compositions for emission in the near UV and visible parts of the electromagnetic spectrum. FIG. 35 shows the AFM surface morphology of GaN / AlGaN MQW grown on GaN textured template VH129. The surface morphology and texture did not change during the deposition of MQWs. In other words, MQWs conformally coated the surface of the template.

Photoluminescence of GaN / AlGaN multiple quantum wells on textured GaN templates grown along the polar direction
The photoluminescence spectrum for one GaN (7 nm) /Al0.2Ga0.8N (8 nm) MQW structure grown on the GaN textured template VH082504-129 (FIG. 28) is shown in FIG. As can be seen from the data, the luminescence intensity from MQWs is significantly higher than that of the GaN textured template. In particular, the peak intensity ratio is 14. Furthermore, the radiation from MQWs is blue shifted compared to the radiation from the GaN textured template.

In FIG. 37, the photoluminescence spectra for the same GaN / AlGaN MQWs grown by MBE on textured and atomically flat GaN templates are shown. Inset (a) shows on a larger scale the photoluminescence spectrum from MQWs grown on a flat GaN template. The main peak in the photoluminescence spectrum from the flat template is due to the photoluminescence from the template itself. The photoluminescence from MQWs was quenching by QCSE present in MQWs grown along polarity (0001). The luminescence spectrum from MQWs on a flat GaN template is shown in inset (b), in which low voltage (4KV) cathodoluminescence (CL) was used to probe as close to the surface as possible. From the inset, the center point of the luminescence peak of MQWs was found at 396 nm. If the count from MQWs on the flat template is estimated to be about 5000, and if the photoluminescence peak intensity from MQWs on the textured template is 3.50 × 10 ⁶ The ratio is about 700.

  To understand this very significant increase in photoluminescence intensity from GaN (5 nm) /Al0.2Ga0.8N (8 nm) MQWs grown on GaN textured templates, spot cathodoluminescence measurements are Run from a fresh sample. In particular, the cathodoluminescence spectrum was measured by focusing the electron beam on the flat region (approximately (0001) orientation) and tilted region of the sample as shown in FIG. This figure represents a cross section of the surface along a certain direction. The cathodoluminescence spectrum taken at points A to C shown in FIG. 38 is shown in FIG. FIG. 39 (a) shows the cathodoluminescence spectrum from a large irradiation area (60 μm × 40 μm). The two peaks at 356 nm and 375 nm are due to luminescence from a quantum well (356 nm) that is not perpendicular to the (0001) polarity direction and a quantum well (375 nm) that is approximately perpendicular to the (0001) polarity direction. The 356 nm peak is blue shifted with respect to the bulk GaN cathodoluminescence peak (364 nm), whereas 375 nm is red shifted. The red shift of the 375 peak and its weak intensity can also be explained by the internal electric field due to the polar effect that distorts MQWs. This phenomenon is QCSE. FIG. 39 (b) shows a spectrum from a point irradiation region on a semi-flat region of MQWs as shown in FIG. As expected, the 382 nm luminescence is from a distorted quantum well by QCSE. The smaller peak at 359 nm is due to the minute roughness on the flat surface, so the small part of the quantum well surface is not perpendicular to (0001). FIG. 39 (c) shows the cathodoluminescence spectrum taken from point B in FIG. In this case, the spectrum separates into two peaks, one due to the emission from the GaN template is from MQW radiation at 356 nm and the other is from the MQW emission at 364 nm. Furthermore, the data support that MQWs whose surface is not perpendicular to the (0001) direction show luminescence that is blue-shifted with respect to the bulk and have intense luminescence due to a significant decrease in QCSE. FIG. 39 (d) shows the cathodoluminescence spectrum from point C in FIG. Furthermore, luminescence occurs at 356 nm, consistent with QW radiation that is not bothered by QCSE.

Formation of GaN pn-junction LED structure on textured GaN template grown along the polar direction Thickness ~ 0.5μm highly conductive Mg-doped p-GaN (hole density -10 ¹⁸ cm ^-3 ) is is n- type automatic doping (electron density to 10 ¹⁹ cm ^-3 is representative) are deposited by MBE on top of textured GaN template. The p-type GaN film was formed using an RF plasma source that activates molecular nitrogen and a Nudesen efflux cell that evaporates Ga and Mg. The growth was done under excessive Ga-rich conditions, which helped Mg uptake at relatively high substrate temperatures (700 ° C.-800 ° C.). As an alternative, p-type layers could be grown using NH ₃ as a nitrogen source. Similar p-type layers could also be grown by MOCVD or HVPE methods. FIG. 12 shows the wafer level electroluminescence spectrum of a GaN pn junction structure made on a textured GaN template. This spectrum was taken at room temperature under 80 mA current injection.

Growth and properties of GaN / AlGaN MQW LEDs The majority of the III nitride studies reported in this document are based on heteroepitaxial growth of these materials on (0001) sapphire or 6H-SiC substrates by various deposition methods. Including. Materials and devices grown on these substrates contain a high density of threading defects (dislocations and translocation domain boundaries). Furthermore, the (0001) orientation is the polar direction in the non-centrosymmetric wurtzite structure, which creates an internal electric field in the heterostructure due to spontaneous and piezoelectron polarities. While such polar effects may be desirable in some types of devices (eg, piezoelectron doping in FETs), radiation based on QCSE multiple quantum well (MQW) structures is undesirable. This effect results in a red shift in QW radiation due to quantum well strain, and also results in a decrease in quantum efficiency because the electron and hole wavefunctions are separated in space. (See Figure 40a)

  Homoepitaxial growth is demonstrated for GaN / AlGaN MQW on a free-standing (10-10) GaN substrate (M-plane), leading to a film along the (11-20) direction sapphire (10-12) (R The same applies to the same MQWs grown on the-surface. Both directions (10-10) and (11-20) have polarity vectors in the plane of MQWs. As shown in FIG. 40b, the photoluminescence peak position of AlGaN / GaN MQWs follows a square well behavior for MQWs grown along the nonpolar direction while similar MQWs with a polar direction show a significant red shift. . The luminescence emission efficiency was about 20 times greater for QWs grown along the non-polar direction for quantum wells with a thickness of 5 nm or more.

Growth and characteristics of GaN templates by HVPE
The growth and characteristics of HVPE GaN templates have been reported by Caval et al., But are incorporated herein by reference in their entirety.

GaN templates (with both flat and randomly textured surfaces) were grown under high growth rate conditions in the range of 30-200 μm / hour, which has NH ₃ / III precursor flow ratios Controlled by 10 to 300. During the template growth, a three-stage growth method was used. This consisted of a GaCl pretreatment step at 1000 ° C., followed by growth of a low temperature GaN buffer at a temperature between 550 ° C. and 650 ° C., and finally a growth of a high temperature GaN epilayer.

  The template was characterized by scanning electron microscope (SEM), photoluminescence, reflectance and Hall effect measurements. Photoluminescence measurements were made using a He—Cd laser as the excitation source, while reflectance measurements were made using a 150 W xenon lamp as the broadband light source.

  FIG. 8 shows SEM images of flat (FIG. 8b) and textured (FIG. 8a) GaN templates. These images were taken with samples tilted 30 ° with respect to the electron beam. The degree of surface texture on the template was found to be due to the amount of GaCl reaching the growth front, which also controls the growth rate of the film. The atomic force microscope surface morphology of the flat GaN template is shown in FIG. 8c. As can be seen from the results, the film was atomically flat and was grown under the step flow growth mode.

FIG. 41a shows a 100 μm ² AFM scan of the textured template surface. A depth analysis of the AFM data (FIG. 41b) shows a Gaussian distribution (random distribution) of the surface roughness. GaN templates with varying degrees of surface texture were produced with average depths ranging from 800 nm to 3 μm.

  The reflectance of the textured template described in FIG. 8a was measured to be less than 1% between 325 nm and 700 nm. That is, almost all incident light from the broadband light source is combined with the GaN textured template. This should be contrasted with the reflectivity of a flat film that is about 18%.

  The electron mobility versus electron concentration for the textured template that was investigated is shown in FIG. As can be seen from the data, all of these GaN templates are thick and auto-doped to n-type and are therefore suitable for the bottom contact layer in GaN LEDs.

  The room temperature photoluminescence (PL) from two GaN templates grown by the HVPE method, one with an atomically flat surface and the other with a randomly textured surface, is shown in FIG. Indicated. Two samples were measured under the same conditions using a 10 mW He-Cd laser. The peak photoluminescence intensity of the sample with the textured surface was approximately 55 times greater than the photoluminescence of the sample with the flat surface.

  The significant increase in photoluminescence intensity from the randomly textured GaN surface is partly attributed to the increased light extraction through the textured surface. Due to the random texturing of the surface, there is an increased escape probability of a single photon because the escape cone is not limited by what is defined by the refractive index of the semiconductor and air. This is because the refractive index in the textured template gradually changes along the optical axis from a value of 2.5 corresponding to GaN to 1.0 corresponding to air. In other words, there is an additional escape angle available for each emitted photon due to the random texture of the interface. This is similar to transmission through a diffraction grating, which gives the incident wave a phase shift and bends the wavefront at a certain angle depending on the wavelength of the incident light (9). In this case, the phase shift is controlled by a periodic change (or periodic surface texture) of the thickness of the grating material at the grating / air interface. In the case of textured GaN templates, the surface texture is not periodic but random, which results in a random phase shift across the interface. This leads to a randomization of the escape angle that effectively increases the photon escape potential. Thus, the surface texture allows a larger escape angle that is not within a critical angle defined with a flat interface as illustrated in FIG. 43b.

  If the extraction efficiency of the synchrotron radiation from the textured GaN template is 100%, then the light from the textured and flat template under the assumption of equal IQE of the flat texture template The ratio of luminescence intensity should have been 25. However, the data shown here shows that this ratio is equal to 55. This means that the IQE of the textured GaN template should be at least twice as high as that of the flat GaN template. The IQE from a textured template should actually be more than twice that of a flat template, as it is unlikely that the extraction efficiency from a textured template will be exactly 100%. . Theoretically, the disorder associated with the textured surface leads to some potential variation, so that excitons are trapped at the localized potential minimum. This leads to the possibility of increased spontaneous emission due to exciton localization.

Growth and characteristics of GaN / AlGaN MQWs by MBE on GaN templates with different surface textures Growth and characteristics of GaN / AlGaN MQWs by MBE on GaN templates with different surface textures are described by Cabal et al. Is hereby incorporated by reference.

  Ten pairs of GaN / Al0.2Ga0.8N MQW with MBE on both textured and flat GaN templates with a substrate temperature of 750 ° C., a well thickness of 7 nm and a barrier thickness of 8 nm. Deposited. An AFM study of MQWs on textured templates shows that MQWs covered conformally textured GaN templates.

  The X-ray diffraction pattern around the (0002) Bragg peak for 10-period GaN (7 nm) /Al0.2 Ga0.8N (8 nm) MQWs grown on a GaN textured template is shown in FIG. This figure shows further evidence that MQWs can be formed on randomly textured templates as shown by the appearance of primary and higher order superlattice peaks. Furthermore, observation of these peaks indicates a steep interface between the AlGaN barrier and the GaN well. FIG. 44 also shows the simulation results using a dynamic distribution model. Assuming that the AlGaN barrier and GaN well have equal growth rates, the simulation results determined a period of 15.4 nm corresponding to a barrier width of 8.2 nm and a well width of 7.2 nm. From the position of the zero order superlattice peak and assuming the effectiveness of Vegard's law in this material system, the Al composition in the AlGaN barrier was determined to be up to 20%. This value is consistent with the desired thickness (8 nm barrier and 7 nm well width) and the alloy composition during growth (20% Al).

  Photoluminescence spectra from MQWs grown on flat and textured GaN templates are shown in FIGS. 11 and 12, respectively. The photoluminescence spectrum from MQWs grown on a flat GaN template (FIG. 11) shows mainly photoluminescence from the 364 nm GaN template with a very small and broad luminescence peak at about 396 nm. It was. Furthermore, the proof that this small peak is due to luminescence from QWs was shown by measuring the cathodoluminescence spectrum of the same sample using a low acceleration voltage (4 KV) to explore QWs. These data are shown in the inset of FIG. In fact, the data show that in addition to luminescence from the 364 nm GaN template, the broad peak occurring at 396 nm corresponds to cathodoluminescence from QWs. Thus, the luminescence from QWs is red-shifted with respect to the bulk and is significantly reduced in size. Both of these results are consistent with the quantum confined Stark effect (QCSE) because these QWs are perpendicular to the (0001) polarity direction.

  FIG. 12 shows the photoluminescence spectrum from MQWs grown on the textured GaN template. For comparison, the photoluminescence spectrum from a textured GaN template is shown in the same figure. It is important to note that the photoluminescence spectrum from MQWs is blue-shifted with respect to the bulk GaN photoluminescence spectrum and that the luminescence intensity is significantly higher than that from the textured GaN template. . Both of these results are consistent with a square quantum well. In other words, since the quantum wells in the textured GaN template are not perpendicular to the (0001) direction, they are not distorted by an internal electric field related to polarity.

  A direct comparison of the peak photoluminescence of MQWs in FIGS. 11 and 12 shows that the photoluminescence intensity from pleated MQWs is ˜700 times higher than that from flat MQWs. This significant increase in photoluminescence from pleated MQWs is due in part to increases in light extraction through textured surfaces and increases in spontaneous emission rates. If the rise from light extraction from the textured surface is assumed to be a factor 25 times higher than that from the flat surface, an additional factor of about 30 times, which must be due to a rise in spontaneous radiation velocity Exists. The evidence discussed above suggests that the increase in IQE is due to a decrease in QCSE, since the quantum well is not perpendicular to the polar (0001) direction. Further increases in IQE are expected due to quantum carrier limitations from wedge-shaped electron eigenmodes. The latter has its origin in the transition in the 2D to 1D carrier behavior due to the V-shaped intersecting plane of the quantum well, whereby the wedge shape behaves as a quantum string, which results in exciton localization and trapping.

White LED without phosphor
This example describes how to make GaN based white LEDs or various colored LEDs without using an emitter such as phosphorus.

  FIG. 14a shows the spectrum of a commercially available white LED taken from Lumileds Technical Data Sheet DS25. This white LED is based on a nitride LED structure that excites a YAG phosphor that emits approximately 430 nm and emits a broad spectrum with a peak at 550 nm. LED structures fabricated based on textured InGaN / GaN MQWs were grown on textured GaN templates fabricated by HVPE. These LEDs have the same spectrum as shown in FIG. 14a without the use of phosphors.

  FIG. 14b shows the electroluminescence spectrum of such an LED. The spectrum was measured under a DC injection current of 30 mA. These spectra have significant similarities to the spectrum of the commercially available white LED shown in FIG. 14a, even though the phosphor was not used for the generation of broad emission at 537 nm. FIG. 14c shows the LED shown in FIG. 14b with a DC injection current whose spectrum is 25 mA.

  The relative intensity between these two peaks depends on the level of current injection. The high energy band increased with bias current. The same LED could produce different colors because its color depends on the relative ratio of the two bands. In FIGS. 15a-15c, the spectra of other LED devices exhibiting the same behavior are shown.

  FIG. 16 shows a photograph of an LED structure taken under DC injection as described in FIG. 15b. As expected, the LED has a green color because the green band is more prominent. However, some parts of the wafer emitted blue light.

  In FIG. 17, the dependence of the electroluminescence spectrum on the DC injection current displays two different LEDs. The right LED has a larger proportion of a flat surface.

Making textured templates using MBE
The GaN template was made by plasma-assisted MBE, among which gallium reacts with atomic nitrogen obtained by passing molecular nitrogen through a plasma source. Both samples grew at 825 ° C. Nucleation grows under gallium-rich conditions (gallium flow is greater than active nitrogen flow) yields a flat surface (FIG. 45a), and grows under nitrogen-rich conditions (active nitrogen flow over gallium flow). Was larger except that it produced a randomly textured surface (FIG. 45b).

QCSE dependence on quantum well layer thickness.
Since QCSE is expected to depend on the width of the quantum well layer, the PL spectra of quantum well layers with thicknesses of 5.5 nm and 7.0 nm were investigated. Figures 46a and 46b show the dependence of the emission peak and luminescence intensity, respectively, on the well width of both flat and textured GaN / Al0.2Ga0.8N MQWs. Looking at FIG. 46a, the PL spectrum from flat MQWs was red-shifted, but the PL spectrum from textured MQWs was slightly blue-shifted with respect to bulk GaN emission. Correspondingly, the PL intensity from flat MQWs increased with decreasing well width, whereas there was only a slight increase from textured MQWs as shown in FIG. 46b. These results are qualitatively consistent with QCSE.

Effects of internal electric field and polarity in the quantum well layer Spontaneous light emission increase in the inclined part of the quantum well layer is due to the transition of the carrier behavior from 2D to 1D (and possibly 0D) by the V-shaped crossing plane of the quantum well. Explained by Thus, the tilted portion can behave as a quantum string (quantum dot) that causes exciton localization and capture. Furthermore, as shown in FIG. 47a, due to the polar component parallel to the quantum well layer, accumulation of electrons in the wedge-shaped portion is expected as shown in FIG. 47b. Due to the equilibrium charge density in these wedges, an increase in spontaneous emission can result from the plasmon effect.

  Although the present invention has been described herein with reference to a preferred embodiment, those skilled in the art will recognize variations, equivalents to the apparatus and methods referred to herein after reading the foregoing specification. Substitutions and other changes can be made. Each of the above-described embodiments can include or incorporate such variations disclosed with respect to any or all of the other embodiments. Therefore, the protection afforded by the patent is intended to be limited in scope only by the definitions contained in the appended claims and their equivalents.

Figure 2 is a partial representation of a textured template of the present invention. 2 is a partial representation of a semiconductor layer deposited on the textured template of FIG. 1 to form a pn junction. 2 is another partial representation of a semiconductor layer deposited on the textured template of FIG. 1 to form a pn junction. 2 is a partial representation of multiple quantum wells and semiconductor layers deposited on the textured template of FIG. FIG. 3 is another partial representation of multiple quantum wells and semiconductor layers deposited on the textured template of FIG. A partial representation of a substrate having a textured surface, which textures a semiconductor layer comprising multiple quantum wells deposited thereon. Another partial representation of a substrate having a textured surface, which textures a semiconductor layer comprising multiple quantum wells deposited thereon. A partial representation of a substrate having a textured surface on which a textured semiconductor layer comprising multiple quantum wells is deposited. Another partial representation of a substrate having a textured surface on which a textured semiconductor layer comprising multiple quantum wells is deposited. FIG. 4 is yet another partial representation of a substrate having a textured surface on which a textured semiconductor layer comprising multiple quantum wells is deposited. Transmission electron microscope (TEM) view of a textured GaN / AlGaN composite quantum well grown on a textured GaN template. A radiating electrically excited GaN wafer level LED with InGaN composite quantum well (MQW). 1 is a scanning electron microscope (SEM) image of a textured gallium nitride (GaN) template of the present invention. It is a SEM image of a normal flat GaN semiconductor layer. FIG. 8b shows the surface morphology of the flat GaN template of FIG. 8b by atomic force microscopy (AFM). FIG. 9 is a photoluminescence comparison between a conventional GaN layer and the textured template of FIG. 8a. FIG. 8a is an atomic force microscope (AFM) image of the textured template of FIG. Figure 5 shows a depth analysis plot of the imaging region. 2 shows the photoluminescence spectrum of a normal flat quantum well. FIG. 8b shows the photoluminescence spectrum of a textured quantum well grown on the textured template of FIG. 8a. Fig. 8b shows the electroluminescence spectrum of a pn junction LED device with the textured template of Fig. 8a. The emission spectrum of a commercially available white LED (Lumireds LXHL-BW02 and technical data sheet DS25) is shown. Electroluminescence spectrum of the inventive LED (textured InGaN composite quantum well (MQW) grown on a textured GaN template manufactured by HVPE) measured at 30 mA DC (direct current) injection current Indicates. FIG. 14b shows the radiant white GaN LED of FIG. 14b with a DC (direct current) injection current of 25mA. FIG. 15 shows an electroluminescence spectrum of an LED similar to that used to obtain the data of FIG. 14b, using an indication of DC injection current. Fig. 14 shows another electroluminescence spectrum of an LED similar to that used to obtain the data of Fig. 14b, using an indication of DC injection current. FIG. 14 shows yet another electroluminescence spectrum of an LED similar to that used to obtain the data of FIG. 14b using a DC injection current reading. 15b is a photograph of an LED under the conditions described in FIG. 15b, showing that some parts emit blue light while many of the wafers emit green light. Figure 5 shows the electroluminescence spectrum of an LED structure taken from parts of a wafer with different textures. The DC injection current is listed on the right side of each graph in the same order as the corresponding curve. Atomic force microscope (AFM) image of a 50 micron thick atomically flat GaN template grown by HVPE. This is a process in which the visible light stripe approximately corresponds to a change in thickness of 2 mm. 1 is a schematic cross-sectional view of an LED embodiment. Schematic of HVPE reactor. Reflectance spectrum of randomly textured GaN template grown via HVPE. Figure 3 shows the photoluminescence effect of several GaN templates with flat and different degrees of textured surfaces. Figure 2 shows the photoluminescence effect of two GaN templates with flat and textured surfaces and the same carrier concentration. The surface texture obtained with the GaN film grown on the R surface of sapphire (1-102) by HVPE is shown. FIG. 24 shows the refractive power of the textured surface described in FIG. The surface morphology of the textured GaN template (VH81) by atomic force microscopy (AFM) is shown. Analysis of the roughness of the textured template of FIG. 25a. FIG. 25a shows the depth analysis of the textured template in FIG. 25a. Fig. 25a shows the spectral density analysis of the textured template in Fig. 25a. The surface morphology of the textured GaN template (VH129) by atomic force microscope (AFM) is shown. Analysis of the roughness of the textured template of FIG. 27a. FIG. 27a shows the depth analysis of the textured template in FIG. 27a. FIG. 27a shows the spectral density analysis of the textured template in FIG. 27a. The surface morphology of a GaN template (VH63) textured by an atomic force microscope (AFM) is shown. Analysis of the roughness of the textured template of FIG. 29a. FIG. 29a shows a deep analysis of the textured template in FIG. 29a. FIG. 29a shows the spectral density analysis of the textured template in FIG. 29a. The surface morphology of the textured GaN template (VH119) by atomic force microscopy (AFM) is shown. Analysis of the roughness of the textured template of FIG. 31a. FIG. 31b shows a depth analysis of the textured template in FIG. 31a. Fig. 31b shows the spectral density analysis of the textured template in Fig. 31a. FIG. 25a shows the photoluminescence spectrum of a GaN template with different rms (root mean square) roughness as described. FIG. 27a shows the photoluminescence spectrum of a GaN template with different rms roughness as described. FIG. 29a shows the photoluminescence spectra of GaN templates with different rms roughness as described. FIG. 31a shows the photoluminescence spectrum of a GaN template with different rms roughness as described. Figure 26 shows the peak intensity versus rms roughness for the textured template in Figures 25a, 27a, 29a, and 31a. AFM surface morphology of GaN / AlGaN MQW grown on GaN textured template (VH129) is shown. Figure 7 shows a roughness analysis of GaN / AlGaN MQW grown on a GaN textured template (VH129). FIG. 4 shows the photoluminescence spectra for the GaN (7 nm) /Al0.2Ga0.8N (8 nm) MQW structure and GaN textured template (VH129, see FIG. 28) used to grow the MQW structure. Figure 2 shows photoluminescence spectra for the same GaN / AlGaN MQW grown by molecular beam epitaxy (MBE) in textured and atomically flat GaN templates. Fig. 40 schematically illustrates the type of surface location used for cathodoluminescence shown in Fig. 39; 39 shows the cathodoluminescence spectrum taken at points A to C shown in FIG. The effect of quantum well strain is shown. Figure 3 shows photoluminescence peaks of AlGaN / GaN MQW grown along non-polar (M-plane) and polar (C-plane) directions. Figure 2 shows an atomic force microscope (AFM) scan of a textured template surface. FIG. 40 shows a depth analysis of the AFM data from FIG. 41a. Figure 6 shows a plot of electron mobility versus electron concentration for a textured GaN template. Illustrates the analysis of photon leakage potential for a flat surface. Illustrates the analysis of photon leakage potential for textured surfaces. Figure 7 shows the X-ray diffraction pattern around the (0002) Bragg peak for 10-period GaN (7nm) /Al0.2Ga0.8N (8nm) MQW grown on a GaN textured template. Flat GaN template tuned by MBE. Randomly textured GaN template adjusted by MBE. The textured random surface of FIG. 45b was generated by growing GaN films under nitrogen rich conditions. Figure 2 shows photoluminescence emission peaks for quantum well layers of different thicknesses. The luminescence intensity for quantum well layers of different thickness is shown. Polarity and internal field effect in pleated quantum well layers. The electron accumulation at the bottom of the inclined part of the quantum well layer with pleats is shown. A schematic representation of an embodiment of a variable color indicator. 1 is a schematic representation of an embodiment of a variable color illumination device. A schematic representation of an embodiment of a color display. A schematic representation of an embodiment of a color projector.

Explanation of symbols

2 substrate 3 pn junction 4a AlN template 4b n-doped AlGaN layer 5 barrier layer 7 quantum well layer 8a p-doped AlGaN layer 8b p-doped GaN layer 9 textured layer 11, 13 Electrode [Cited document]
1. Cabal et al. “Intensified light extraction and spontaneous emission from textured GaN templates formed during growth by HVPE method” Technology program in compound semiconductor XLI and nitride and wide bandgap semiconductors, sensors and electronics V State, Electrochemical Society Preceding, 2004-06, page 351.
2. Caval et al. “Elevated light extraction and spontaneous emission from pleated quantum wells grown by plasma-assisted molecular beam epitaxy (PAMBE)” lecture at the 22nd North American Molecular Beam Epitaxy Conference, Banff, Alberta, Canada, October 10- 13th, 2004, 110 pages.
3. Ayer et al. "Growth and characteristics of nonpolar (11-20) GaN and AlGaN / GaN MQWs on R-plane (10012 sapphire)" Mater. Res. Soc. Symp. Proc., 743, L3.20, (2003 Year).
4). Liu et al., IEEE Journal of Selective Topics in Quantum Electronics, Vol. 8, 231 (2002).
5. Tuao, J., “Light Emitting Diodes (LEDs) for General Lighting” OIDA Technology Roadmap Update (2002).
6). Windish et al., "LEDs with 40% efficient thin film surface texture by natural lithographic optimization," IEEE Trans. Electron Devices, 47, 1492, (2000).

Claims (41)

A semiconductor device used as an emitter,
A substrate made of a material selected from the group consisting of sapphire, silicon carbide, zinc oxide, silicon, gallium arsenide, gallium nitride, aluminum nitride and aluminum gallium nitride;
A first layer on the substrate, the first layer comprising a group III nitride semiconductor and having a topology in which the surface of the first layer is randomly textured;
The first layer is n-type doped, and the first layer is electrically coupled to the first contact;
One or more quantum well layers alternating with the barrier layers and textured by the surface of the first layer;
The barrier layer is made of a group III nitride semiconductor, and the quantum well layer is made of a group III nitride semiconductor.
The upper layer is made of a group III nitride semiconductor, the upper layer is textured by the surface of the adjacent quantum well layer, the upper layer is p-type doped, the upper layer is electrically coupled to the second contact, and the device The electroluminescence spectrum of the semiconductor device is controlled by passing current through the device between the first and second contacts.   The semiconductor device according to claim 1, wherein a surface of the substrate is randomly textured, and the first and subsequent layers replicate the textured surface of the substrate.   The substrate is (0001) sapphire, (10-12) sapphire, (10-10) sapphire, (11-20) sapphire, (0001) silicon carbide, (0001) zinc oxide, (111) silicon, (111) 2. The semiconductor device according to claim 1, wherein the semiconductor device is made of a material selected from the group consisting of gallium arsenide, (0001) gallium nitride, (0001) aluminum nitride, and (0001) AlGaN.   The semiconductor device according to claim 1, wherein the substrate has a surface textured on a side facing the first layer.   The semiconductor device according to claim 1, wherein the substrate has a textured surface on a side away from the first layer.   The semiconductor device according to claim 1, wherein the substrate comprises a surface polished toward the side facing the first layer.   The semiconductor device according to claim 1, wherein the surface of the substrate is textured by lithography or etching.   The first layer is a deposition on the substrate resulting from one of hydrogenated vapor phase epitaxy, metal-organic chemical vapor deposition, molecular beam epitaxy, liquid phase growth, laser ablation, or a combination of these methods. The semiconductor device according to claim 1.   9. The semiconductor device of claim 8, wherein the first layer is the result of hydrogen vapor phase epitaxy of a group III nitride semiconductor material in the presence of excess HCl thereon. The semiconductor device according to claim 9, wherein a molar ratio of NH _{3 to} HCl in the process of hydrogenated vapor phase epitaxy is 5: 1 to 10: 1.   The semiconductor device according to claim 9, wherein the quantum well layer and the barrier layer are a result of molecular beam epitaxy.   The semiconductor device according to claim 8, wherein the first layer is a result of molecular beam epitaxy in the presence of molecules N in excess of Ga.   The one or more quantum well layers are grown by hydrogenation vapor phase epitaxy, metal organic chemical vapor deposition, molecular beam epitaxy, liquid phase growth, laser ablation, or a combination of these methods. 2. The semiconductor device according to 1.   The semiconductor device according to claim 1, wherein the electroluminescence spectrum of the device comprises two or more peaks.   15. The semiconductor device according to claim 14, wherein the multiple quantum well is composed of scattered regions having quantum well layers having different thicknesses.   The semiconductor device according to claim 15, wherein the quantum well layer in the flat region of the multiple quantum well is thicker than the quantum well layer in the inclined region of the multiple quantum well.   The semiconductor device according to claim 14, wherein one of the peaks is in the range of 390 to 450 nm and the other peak is in the range of 500 to 600 nm.   The semiconductor device of claim 14, wherein an increase in current through the device between the first and second contacts increases electroluminescence at one of the peaks compared to the other.   The semiconductor device according to claim 18, wherein the increasing peak is in a range of 390 to 450 nm.   19. The semiconductor device of claim 18, wherein the electroluminescence coloring temperature is blue shifted by increasing the current through the device between the first and second contacts.   2. The semiconductor device according to claim 1, wherein the electroluminescence is white.   2. The semiconductor device according to claim 1, wherein the electroluminescence is based on a coloring temperature in a range of 2500 ° to 7500 ° K. 3.   The semiconductor device according to claim 1, further comprising a phosphor.   24. The semiconductor device according to claim 23, wherein the phosphor has an emission peak in the range of 500 to 700 nm. A substrate made of a material selected from the group consisting of sapphire, silicon carbide, zinc oxide, silicon, gallium arsenide, gallium nitride, aluminum nitride, and aluminum gallium nitride;
A first layer on the substrate comprising a group III nitride semiconductor, wherein the surface of the first layer has a randomly textured topology, the first layer is n-doped, and the first layer Is electrically coupled to the first contact,
One or more quantum well layers alternating with the barrier layers and textured by the surface of the first layer, the barrier layers comprising a III nitride semiconductor and the quantum well layers comprising a group III nitride semiconductor Become
A top layer comprising a group III nitride semiconductor, wherein the top layer is textured by the surface of the quantum well layer furthest from the first layer, the top layer is p-type doped, and the top layer is Electrically coupled to two contacts,
It has a light emitting diode consisting of these things,
Passing an electric current through the device between the first and second contacts, the electroluminescence spectrum of the diode comprising a step controlled by the current, controlling the emission spectrum of the light emitting diode Method.   The electroluminescence spectrum of the diode consists of two or more peaks, and an increase in current through the device between the first and second contacts results in electroluminescence at one of the peaks compared to the other. 26. The method of claim 25, wherein the method increases.   27. The method of claim 26, wherein the peak electroluminescence in the 390-450 nm range is increased relative to one or more other peaks.   27. The method of claim 26, wherein the electroluminescent coloring temperature is blue-shifted by increasing the current through the device between the first and second contacts.   A variable colored display comprising the semiconductor device of claim 1 and a controller for adjusting current through the device between the first and second contacts in response to an input signal, wherein the change in the input signal is A variable coloring indicator that occurs when the color of light emitted by the device changes.   A change in input signal comprising one or more semiconductor devices according to claim 1 and a controller for adjusting a current through each of the devices between said first and second contacts in response to one or more input signals. Is a variable colored lighting device that produces a change in intensity and color of light emitted by the device.   The lighting device according to claim 30, wherein the plurality of semiconductor devices are arranged in an array.   The lighting device according to claim 30, comprising a plurality of the semiconductor devices, wherein each semiconductor device is independently controlled.   The lighting device according to claim 30, comprising a plurality of the semiconductor devices, wherein the semiconductor devices are controlled in harmony.   A two-dimensional array comprising a plurality of semiconductor devices of claim 1 and a controller for adjusting current through each semiconductor device between said first and second contacts in response to an input signal, wherein the input signal is a semiconductor device. A two-dimensional colored display device that causes the formation of a luminescent colored mold.   35. A colored display device according to claim 34, wherein the colored mold forms an image that is visible by inspection with an array.   36. The display device according to claim 35, which forms a still image.   36. The display device according to claim 35, which forms a moving image.   A projector comprising: a two-dimensional array comprising a plurality of semiconductor devices according to claim 1; and a controller for adjusting a current through each semiconductor device between said first and second contacts in response to an input signal. A projector in which a signal is produced by a semiconductor device in the form of a colored light emission and projected on a projection screen.   40. The projector of claim 38, wherein the color pattern forms an image on the projection screen.   40. The projector of claim 38, which is a still image projector.   40. The projector of claim 38, which is a movie projector.

Images